For example, in a steam generator as a heat exchanger used in a pressurized water reactor (PWR), both ends of a number of inverted U-shaped heat transfer tubes are inserted through and fixed to tube plates inside a core barrel section thereof. This heat transfer tube is inspected for its soundness. Such an inspection includes an inspection for a seal-welded portion at a portion where the heat transfer tube is opened to the tube plate.
A defect (a flaw or the like) at the seal-welded portion may possibly be a cause for the formation of a path (leak path) from a primary cooling water side to a secondary cooling water side. Thus, an inspection for the seal-welded portion is performed when manufacturing the steam generator. Moreover, also during a periodic inspection performed after the service of the steam generator, there is a possibility for inspecting the seal-welded portion.
An eddy current testing (ECT) may be employed for this inspection since it can inspect a defect present on a surface of the seal-welded portion relatively at a high speed. Various methods have been suggested conventionally (for example, see Patent Literatures 1 and 2).
Moreover, there exist a large number of heat transfer tubes in the steam generator. Therefore, it takes a large amount of time for a worker to manually perform an inspection for such heat transfer tubes, and it is also a troublesome work. Thus, an increase in inspection speed and automation by a remote control are desired. Furthermore, during a periodic inspection performed after the service of the steam generator, since the inside of a water chamber to which the heat transfer tubes are opened is in a radiation atmosphere by being directly in contact with primary cooling water heated in the reactor, it is not preferable for a worker performing the inspection to stay in the water chamber for a long period of time. Thus, it is preferred to perform the inspection by a remote control from the outside of the water chamber. Conventionally, there has been suggested an inspection robot configured to be supported by a tube plate surface via a clamp mechanism inserted through a heat transfer tube and to be movable along the tube plate surface (for example, see Patent Literatures 3 and 4).